1 The Linux LAPB Module Interface 1.3
2 3 Jonathan Naylor 29.12.96
4 5Changed (Henner Eisen, 2000-10-29): int return value for data_indication()
6 7The LAPB module will be a separately compiled module for use by any parts of
8the Linux operating system that require a LAPB service. This document
9defines the interfaces to, and the services provided by this module. The
10term module in this context does not imply that the LAPB module is a
11separately loadable module, although it may be. The term module is used in
12its more standard meaning.
13 14The interface to the LAPB module consists of functions to the module,
15callbacks from the module to indicate important state changes, and
16structures for getting and setting information about the module.
17 18Structures
19----------
20 21Probably the most important structure is the skbuff structure for holding
22received and transmitted data, however it is beyond the scope of this
23document.
24 25The two LAPB specific structures are the LAPB initialisation structure and
26the LAPB parameter structure. These will be defined in a standard header
27file, <linux/lapb.h>. The header file <net/lapb.h> is internal to the LAPB
28module and is not for use.
29 30LAPB Initialisation Structure
31-----------------------------
32 33This structure is used only once, in the call to lapb_register (see below).
34It contains information about the device driver that requires the services
35of the LAPB module.
36 37struct lapb_register_struct {
38 void (*connect_confirmation)(int token, int reason);
39 void (*connect_indication)(int token, int reason);
40 void (*disconnect_confirmation)(int token, int reason);
41 void (*disconnect_indication)(int token, int reason);
42 int (*data_indication)(int token, struct sk_buff *skb);
43 void (*data_transmit)(int token, struct sk_buff *skb);
44};
45 46Each member of this structure corresponds to a function in the device driver
47that is called when a particular event in the LAPB module occurs. These will
48be described in detail below. If a callback is not required (!!) then a NULL
49may be substituted.
50 51 52LAPB Parameter Structure
53------------------------
54 55This structure is used with the lapb_getparms and lapb_setparms functions
56(see below). They are used to allow the device driver to get and set the
57operational parameters of the LAPB implementation for a given connection.
58 59struct lapb_parms_struct {
60 unsigned int t1;
61 unsigned int t1timer;
62 unsigned int t2;
63 unsigned int t2timer;
64 unsigned int n2;
65 unsigned int n2count;
66 unsigned int window;
67 unsigned int state;
68 unsigned int mode;
69};
70 71T1 and T2 are protocol timing parameters and are given in units of 100ms. N2
72is the maximum number of tries on the link before it is declared a failure.
73The window size is the maximum number of outstanding data packets allowed to
74be unacknowledged by the remote end, the value of the window is between 1
75and 7 for a standard LAPB link, and between 1 and 127 for an extended LAPB
76link.
77 78The mode variable is a bit field used for setting (at present) three values.
79The bit fields have the following meanings:
80 81Bit Meaning
820 LAPB operation (0=LAPB_STANDARD 1=LAPB_EXTENDED).
831 [SM]LP operation (0=LAPB_SLP 1=LAPB=MLP).
842 DTE/DCE operation (0=LAPB_DTE 1=LAPB_DCE)
853-31 Reserved, must be 0.
86 87Extended LAPB operation indicates the use of extended sequence numbers and
88consequently larger window sizes, the default is standard LAPB operation.
89MLP operation is the same as SLP operation except that the addresses used by
90LAPB are different to indicate the mode of operation, the default is Single
91Link Procedure. The difference between DCE and DTE operation is (i) the
92addresses used for commands and responses, and (ii) when the DCE is not
93connected, it sends DM without polls set, every T1. The upper case constant
94names will be defined in the public LAPB header file.
95 96 97Functions
98---------
99 100The LAPB module provides a number of function entry points.
101 102 103int lapb_register(void *token, struct lapb_register_struct);
104 105This must be called before the LAPB module may be used. If the call is
106successful then LAPB_OK is returned. The token must be a unique identifier
107generated by the device driver to allow for the unique identification of the
108instance of the LAPB link. It is returned by the LAPB module in all of the
109callbacks, and is used by the device driver in all calls to the LAPB module.
110For multiple LAPB links in a single device driver, multiple calls to
111lapb_register must be made. The format of the lapb_register_struct is given
112above. The return values are:
113 114LAPB_OK LAPB registered successfully.
115LAPB_BADTOKEN Token is already registered.
116LAPB_NOMEM Out of memory
117 118 119int lapb_unregister(void *token);
120 121This releases all the resources associated with a LAPB link. Any current
122LAPB link will be abandoned without further messages being passed. After
123this call, the value of token is no longer valid for any calls to the LAPB
124function. The valid return values are:
125 126LAPB_OK LAPB unregistered successfully.
127LAPB_BADTOKEN Invalid/unknown LAPB token.
128 129 130int lapb_getparms(void *token, struct lapb_parms_struct *parms);
131 132This allows the device driver to get the values of the current LAPB
133variables, the lapb_parms_struct is described above. The valid return values
134are:
135 136LAPB_OK LAPB getparms was successful.
137LAPB_BADTOKEN Invalid/unknown LAPB token.
138 139 140int lapb_setparms(void *token, struct lapb_parms_struct *parms);
141 142This allows the device driver to set the values of the current LAPB
143variables, the lapb_parms_struct is described above. The values of t1timer,
144t2timer and n2count are ignored, likewise changing the mode bits when
145connected will be ignored. An error implies that none of the values have
146been changed. The valid return values are:
147 148LAPB_OK LAPB getparms was successful.
149LAPB_BADTOKEN Invalid/unknown LAPB token.
150LAPB_INVALUE One of the values was out of its allowable range.
151 152 153int lapb_connect_request(void *token);
154 155Initiate a connect using the current parameter settings. The valid return
156values are:
157 158LAPB_OK LAPB is starting to connect.
159LAPB_BADTOKEN Invalid/unknown LAPB token.
160LAPB_CONNECTED LAPB module is already connected.
161 162 163int lapb_disconnect_request(void *token);
164 165Initiate a disconnect. The valid return values are:
166 167LAPB_OK LAPB is starting to disconnect.
168LAPB_BADTOKEN Invalid/unknown LAPB token.
169LAPB_NOTCONNECTED LAPB module is not connected.
170 171 172int lapb_data_request(void *token, struct sk_buff *skb);
173 174Queue data with the LAPB module for transmitting over the link. If the call
175is successful then the skbuff is owned by the LAPB module and may not be
176used by the device driver again. The valid return values are:
177 178LAPB_OK LAPB has accepted the data.
179LAPB_BADTOKEN Invalid/unknown LAPB token.
180LAPB_NOTCONNECTED LAPB module is not connected.
181 182 183int lapb_data_received(void *token, struct sk_buff *skb);
184 185Queue data with the LAPB module which has been received from the device. It
186is expected that the data passed to the LAPB module has skb->data pointing
187to the beginning of the LAPB data. If the call is successful then the skbuff
188is owned by the LAPB module and may not be used by the device driver again.
189The valid return values are:
190 191LAPB_OK LAPB has accepted the data.
192LAPB_BADTOKEN Invalid/unknown LAPB token.
193 194 195Callbacks
196---------
197 198These callbacks are functions provided by the device driver for the LAPB
199module to call when an event occurs. They are registered with the LAPB
200module with lapb_register (see above) in the structure lapb_register_struct
201(see above).
202 203 204void (*connect_confirmation)(void *token, int reason);
205 206This is called by the LAPB module when a connection is established after
207being requested by a call to lapb_connect_request (see above). The reason is
208always LAPB_OK.
209 210 211void (*connect_indication)(void *token, int reason);
212 213This is called by the LAPB module when the link is established by the remote
214system. The value of reason is always LAPB_OK.
215 216 217void (*disconnect_confirmation)(void *token, int reason);
218 219This is called by the LAPB module when an event occurs after the device
220driver has called lapb_disconnect_request (see above). The reason indicates
221what has happened. In all cases the LAPB link can be regarded as being
222terminated. The values for reason are:
223 224LAPB_OK The LAPB link was terminated normally.
225LAPB_NOTCONNECTED The remote system was not connected.
226LAPB_TIMEDOUT No response was received in N2 tries from the remote
227 system.
228 229 230void (*disconnect_indication)(void *token, int reason);
231 232This is called by the LAPB module when the link is terminated by the remote
233system or another event has occurred to terminate the link. This may be
234returned in response to a lapb_connect_request (see above) if the remote
235system refused the request. The values for reason are:
236 237LAPB_OK The LAPB link was terminated normally by the remote
238 system.
239LAPB_REFUSED The remote system refused the connect request.
240LAPB_NOTCONNECTED The remote system was not connected.
241LAPB_TIMEDOUT No response was received in N2 tries from the remote
242 system.
243 244 245int (*data_indication)(void *token, struct sk_buff *skb);
246 247This is called by the LAPB module when data has been received from the
248remote system that should be passed onto the next layer in the protocol
249stack. The skbuff becomes the property of the device driver and the LAPB
250module will not perform any more actions on it. The skb->data pointer will
251be pointing to the first byte of data after the LAPB header.
252 253This method should return NET_RX_DROP (as defined in the header
254file include/linux/netdevice.h) if and only if the frame was dropped
255before it could be delivered to the upper layer.
256 257 258void (*data_transmit)(void *token, struct sk_buff *skb);
259 260This is called by the LAPB module when data is to be transmitted to the
261remote system by the device driver. The skbuff becomes the property of the
262device driver and the LAPB module will not perform any more actions on it.
263The skb->data pointer will be pointing to the first byte of the LAPB header.
264